I once heard the argument that generic insulin would not be a good idea, and that it is because of this that the companies that make insulin won't hand out their production and processing plans. While I'm not sure that the pharmaceutical companies will continue with this, I do agree with the fact that generic insulin might cause more problems than it solves.
I can tell you that there's a big difference between some generic pills and their brand-name companions. Even take metformin--I knew the difference between the brands whenever my pharmacy switched me. It didn't affect my BG control (which was pretty bad on met, anyway), but it did affect my GI tract, and I had different and/or worse side effects with different brands. The worst part was that I was often switched every two months, depending on what my pharmacy had available when I renewed my prescription.
Let's take another example. I have a friend who's a severe asthmatic. She told me that the different generic brands for the same medication in an inhaler acted differently with her--possibly based on the particle size of the spray in the different company's inhalers, possibly because of the additives or even a difference in potency. She now refuses to get all but one of the generic brands.
I know other people who share the same sentiment regarding other pills. If you think about the difference between store-brand and name-brand acetaminophen, ibuprofen, even Robitussin--sometimes they're the same, sometimes they're not. That's the potential problem with generic insulin.
Though the manufacturing process is closely monitored, it appears that the generic brands don't have the same motivation in ensuring that all of their products are exactly as good as the original. The name-brands really, really want you to use their drug because they make a huge profit off of it, but the generic brands are producing the same drug for cheaper, and they weren't the ones who put in the original research, either. They therefore have less invested in a "perfect" product. And while the FDA has standards for drugs and drug processing, I'm pretty sure I've heard that the name-brand drug company's processing standards are often higher than the national requirement.
Think about the difference between Novolog and Humalog. They're the "same" drug--insulin--but many people react differently to them. And yes, they're different, but like Brian said, the biologic generics won't be generics, they'll be biosimilars. Therefore, the difference between different generic forms of insulin might be the difference between Novolog and Humalog--or it could be more, or less. It's impossible to tell. And if there are multiple generic forms of insulin available on the market at the same time, you might get a different generic every month, which means an adjustment period every month to what is essentially a new brand of insulin.
I'm not saying that generic insulin is a bad idea, I just think that with something that's already so chancy, it may be difficult to get generics to all be the same with respect to quality, potency, and all the other things we take for granted to be stable in a vial of insulin.